Remember how Mark Shuttleworth justified moving the window titlebar widgets to the left by claiming the space freed up on the right side could now be used for something else? On his blog, Shuttleworth unveiled what, exactly, Ubuntu's plans are: window indicators, or 'windicators'. In a nutshell, it comes down to having a tray area in every window.

The only thing remotely useful to me is per-application volume control. But even without those "windicators," it's just a couple of clicks away to, say, mute the browser with PulseAudio.

A "couple" is more then one. Changing the volume of a single application is very cumbersome with the current pulse controls. Not to mention that the sound control may get hidden by the notification area if it is not used often (at least in KDE; I don't know about Gnome).

As for what is useful to implement as a windicator, that's really a tough question IME toolbars (uim, scim, etc) come into mind if per-application mode is set. However, I am sure application writers will find other, application-specific tidbits to put there.